Methods and devices for mitigating interference with FHSS signals

ABSTRACT

Methods and devices for mitigating interference with a signal of a frequency hopping spread spectrum system are disclosed. A second signal is detected, and a property of the second signal is determined. At least one of a set of designated frequency channels used by the frequency hopping spread spectrum system is determined as having a property most similar to that of the second signal. The usage, by the frequency hopping spread spectrum system, of the at least one most similar designated frequency channel is then modified, for communication of data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of the following patent applicationswhich are hereby incorporated in their entirety by reference: GB1315696.3 filed Sep. 4, 2013 and GB 1320073.8 filed Nov. 13, 2013.

FIELD OF THE INVENTION

This invention is directed to methods and devices for mitigation,avoidance or prevention of interference with frequency hopping spreadspectrum (FHSS) signals and other radio signals, such as direct sequencespread spectrum (DSSS) or Wi-Fi signals.

BACKGROUND TO THE INVENTION

Radio frequency transmissions take many forms, and some are particularlyuseful in wireless networks. In spread spectrum transmissions a signalis spread over a wider band than the original bandwidth (usually narrowband) of the signal. One example of a spread spectrum transmissionmethod is the frequency hopping spread spectrum (FHSS) method in which anarrow band signal to be transmitted is combined with a carrier whichmakes a sequence of pseudo-random changes or “hops” in frequency. Thesequence is known to the transmitter and receiver, so the originalsignal can be retrieved at the receiver. Another example is the directsequence spread spectrum (DSSS) method in which an original (narrowband) signal is multiplied by a pseudo-random “noise” sequence signal.Again, the sequence is known to transmitter and receiver.

Problems may arise when these types of transmission are attempted inclose proximity, as interference can occur. Interference is particularlylikely to occur if both transmissions are using the 2.4 GHz band, whichmay be desirable for many applications. One previously considered schemefor reducing interference is for the system using FHSS to rule out theuse of any frequencies or channels coinciding with or near thefrequencies or channels of the system using DSSS so that none of thehops will be to a channel or frequency overlapping or nearby one in use.However, this previous scheme is typically used only in low power FHSSsystems (at, for example, 0 dbi—zero antenna gain in decibels-isotropic)where the FHSS signal is unlikely to affect the DSSS signal and cannotbe used for high power signals. In addition, the original signal to betransmitted by these FHSS systems is usually very narrow band, as thebit rate is low (for example, only around 1 Mb required). Higher bitrates cannot be accommodated. Some previous FHSS systems require thesuppression of the DSSS signal when the FHSS system is activated, forexample where the signals are generated by the same apparatus. Theseprevious schemes require that large parts of the bandwidth for FHSS arenot used, as whole channels or frequency ranges near those of the DSSSsignal are ignored.

STATEMENT OF THE INVENTION

In general terms, embodiments of the invention may provide a method formitigating interference with a signal of a frequency hopping spreadspectrum system, comprising: detecting a second signal, determining aproperty of the second signal; determining at least one of a set ofdesignated frequency channels used by said frequency hopping spreadspectrum system as having a property most similar to said property ofsaid second signal; and modifying usage, by said frequency hoppingspread spectrum system, of said at least one most similar designatedfrequency channel, to communicate data.

This method allows actions to mitigate, avoid or prevent interferencebetween the FHSS signal and another signal, without having to stop usingcertain channels for FHSS hopping.

The detection of the second signal may be by scanning, for example usinga scanner, such as a wireless scanner searching for local access points.The second signal may be a DSSS signal, such as one employed in awireless network. Either or both signal(s) may be radio frequencysignals.

The property of the second signal may be a frequency characteristic. Forexample, the characteristic may be the centre frequency, the modulationtype, or the channel width of the second signal (or any combination ofthese).

The determination of the designated frequency channel having a propertymost similar to that of the second signal may be by comparing afrequency of the designated channel with a frequency of the secondsignal (for example, a centre frequency). The determination may find thedesignated channel having the frequency most similar to that of thesecond signal, for example the closest in the spectrum.

The step of modifying usage of the most similar designated frequencychannel may comprise using said most similar designated frequencychannel for a reduced bandwidth for the data.

Modifying usage may comprise processing the data to reduce a databandwidth for communication via said most similar designated frequencychannel. Modifying usage may comprise reducing a bandwidth of said mostsimilar designated frequency channel. The reduced bandwidth may be lessthan 4.5 Mb and, for example, between 250 Kb and 1 Mb.

The method may further comprise reducing a usage of said most similardesignated frequency channel in the frequency hopping spread spectrumsystem. This may be by reducing simply the amount of time the designatedchannel is used for, or the frequency (number of times in the overallcycle) the designated channel is used. For example, a duty cycle of thedesignated channel in the frequency hopping may be reduced.

The method may further comprise: detecting a change in the property ofthe second signal; re-determining the at least one of the set ofdesignated frequency channels having a property most similar to theproperty of the second signal; and modifying usage, by the frequencyhopping spread spectrum system, of the re-determined most similardesignated frequency channel.

The method may further comprise, on detecting the second signal,determining frequencies for each of the set of designated frequencychannels used by the frequency hopping spread spectrum system accordingto the type of the second signal.

Embodiments of the invention may provide a device for mitigatinginterference with a signal of a frequency hopping spread spectrumsystem, said device comprising:

-   -   a module configured to generate a frequency hopping spread        spectrum signal to communicate data; and    -   a scanner configured to detect a second signal; and a processor        configured to: determine a property of said second signal; and        determine at least one of a set of designated frequency channels        used by said frequency hopping spread spectrum module as having        a property most similar to that of said second signal,    -   wherein the module is configured to modify usage of said at        least one most similar designated frequency channel, to        communicate data.

The device may further comprise a module configured to generate afurther signal, additional to the frequency hopping spread spectrumsignal, for communication with a device generating said second signal.

Embodiments of the invention may provide a monitoring apparatuscomprising:

-   -   at least one image capturing module; and    -   a dual mode radio communications device comprising a:        -   a first module configured to generate a first signal to            communicate data derived from said at least one image            capturing module;        -   a second module configured to generate a second signal; a            scanner configured to detect said second signal; and a            processor configured to:        -   determine a property of the second signal; and        -   determine at least one of a set of designated frequency            channels used by the first module as having a property most            similar to that of the second signal,    -   wherein said first signal is generated using a frequency hopping        spread spectrum format, said second signal is generated using a        different signal format to said first signal and said first        module is configured to modify usage of the at least one most        similar designated frequency channel to communicate said data.

The above-described features and embodiments may be combined to providefurther features and embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only withreference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating a dual mode radiocommunications device;

FIG. 2 is a flow chart illustrating examples of methodology formitigating signal interference in a dual mode radio communicationsdevice such as the dual mode radio communications device shown in FIG.1;

FIG. 3 is a schematic diagram showing the dual mode radio communicationsdevice of FIG. 1 in greater detail;

FIG. 4 shows at monitoring apparatus comprising a portable receiver anda monitoring device comprising a dual mode radio communications device;

FIG. 5 is a schematic illustration of the infant monitoring device;

FIG. 6 is a schematic illustration of the portable receiver;

FIG. 7 is a rear elevation of the portable receiver;

FIG. 8 shows the portable receiver in use; and

FIG. 9 shows a modification to the dual mode radio communications deviceillustrated by FIG. 3.

DETAILED DESCRIPTION

The methods and devices described allow modification of the use of thedesignated channels in a frequency hopping spread spectrum system (FHSS)in response to a detected signal or available network, to alleviateinterference problems with other signals. This may allow the FHSS signalto run as efficiently as possible and/or the use of higher band andhigher power signals for the FHSS than are possible under previous FHSSschemes, for example up to 20 dbi and up to 4 Mb. The methods anddevices described may also allow two transmission schemes to work inclose proximity, without one suppressing the other, so that an FHSSmodule and another module, for example a DSSS module, can be housed in adual mode radio communications device, the other module communicatingwith the source of a second signal, for example a wireless access pointor router.

FIG. 1 illustrates a dual mode radio communications device 104. The dualmode radio communications device 104 comprises an FHSS module 106 and aDSSS module 108. The FHSS module 106 is configured to generate, transmitand receive FHSS signals and the DSSS module 108 is configured togenerate, transmit and receive DSSS signals. The dual mode radiocommunications device 104 has an antenna 110 (or one for each type ofmodule) which allows communication wirelessly with other devices. Afirst such device is an FHSS enabled device 112, for example one similarto a Bluetooth™ device, but for higher powered signals and higher bitrates. A second such device is a wireless access point 114, for exampleusing the DSSS scheme. The dual mode radio communications device 104may, for example, access a wireless internet connection through thewireless access point 114.

An example of operation of a dual mode radio communications device suchas the dual mode radio communications device 104 to mitigateinterference with signals using the frequency hopping spread spectrumsystem will now be described with reference to FIG. 2. At 202 a signalpotentially competing with an FHSS signal is detected. In theillustrated example the potentially competing signal is a DSSS signal,but it could be any type of radio signal that might compete forbandwidth or frequencies with the FHSS signal, such as other types ofwireless protocol. The signal may be found by scanning to find anyaccess points in the local area. Scanning may be implemented using awireless scanner. In alternative examples, the scanning may find an adhoc network device.

At 204 a determination is made as to whether the DSSS channel interfereswith any of the FHSS designated channels, i.e. those frequencies thatthe pseudo-random scheme for hopping has chosen. The interference maysimply be due to the DSSS channel and one or more of the FHSS channelsoverlapping. For example, if the Wi-Fi channel is 1 at 2.412 GHz,modulation is 802.11b, 20 MHz bandwidth, any FHSS channels betweenaround 2.409 GHz and 2.415 GHz will likely be affected, and othersnearby.

Determination of the interference may find the centre frequency, themodulation type or the channel width of the second signal (the DSSSchannel), or any combination of them. A similarity measured between thetwo may be a simple difference calculation with one or a combination ofthese features of the competing channel. There may be more than onepotentially competing signal in the area. Therefore detection 202 anddetermination 204 may be repeated for these other signals. For example,there may be an access point that the user is trying to access with adual mode radio communications device using this method and otherwireless network points the user is unaware of, that may neverthelesscause interference. In addition, for wider DSSS bands (22 MHz, 40 MHz)the system may need to alter more channels.

If at 204 it is determined that there is no interference, at 206communications can continue with no modification of the FHSS channels.However, where interference, similarity, overlap or the like isdetected, at 208 one or more of the closest (or all of the) FHSSchannels that may be interfering is modified. This can be done invarious ways, and these can be used in combination.

One option at 210 is to reduce the usage for that/those channel(s). Forexample, the amount of time the designated channel is used for, or thefrequency (number of times in the overall cycle) the designated channelis used may be reduced. One method is to reduce the duty cycle of thedesignated channel in the frequency hopping scheme. This means that theinterfering FHSS channel is used less, and can be reduced to the pointthat any noise induced is insufficient to disrupt the overall signalwhich the FHSS system is attempting to communicate.

Another option at 212 is to modify usage of the closest FHSS channel(s)for reduced bandwidth. This can be done in a number of ways. In oneimplementation, the system can be set so that these channels are onlyused when the system is transmitting a low bandwidth signal, such asaudio only. At other times, the channels may be avoided altogether.

In more complex implementations, the bandwidth of either the channel inconflict, or of the data using it may be reduced. In the former case, ifthe bandwidth of the channel is reduced, there is likely to be lessinterference with any close channels in the competing other (DSSS)signal. The bandwidth may be narrow band, or very narrow band, althoughthe latter may only be usable for audio data. This may be done by anumber of methods and previously considered schemes, for example byre-arranging the data for transmission so that low bandwidth portions ofthe data can be passed using a narrow band channel (i.e. the nownarrowed closest FHSS channel), or to pass less of the data over thatchannel in the frequency hopping scheme, so that a narrow band can beused.

In one example, the narrow band used is 250 Kb to 1 Mb (i.e. 0.125 MHzto 500 MHz, similar to Bluetooth™ FHSS) which may have less interferencewith Wi-Fi. The narrow band usage should be under 4.5 Mb (FCC allows atleast 15 non-overlapping channels, so the maximum bandwidth ispreferably not higher than 4.5 Mb)

In general, narrow band and very narrow band usage are as follows:

-   Narrow Band: 2M RF (40 Non-Overlapping Channels)-   Very Narrow Band: 1M RF (80 Non-Overlapping Channels)

As an example, if the channel used by the Wi-Fi is channel one (e.g.2.412 GHz), the closest clean channels for FHSS may be 2.4095 GHz and2.4145 GHz). Modifying these two channels to narrow band or reducingusage of these two channels (or both) will help mitigate interferencebetween the Wi-Fi and the FHSS.

In addition, the processes illustrated by FIG. 2 can be repeated at anytime, for example to keep updated, or if it is detected that the secondsignal (for example. the DSSS signal) has changed to a different type,or to use different channels. The new channels are detected, and newdeterminations are made as to the closest FHSS channels, and how tomodify them.

In one example, the FHSS system is primed only to use designatedchannels which are usually free from interference, such as those whichtypically are not used or fall between common DSSS implementations. Forinstance, the frequency between a common first and second channel Wi-Fiimplementation is (2.412 GHz+2.417 GHz)/2=2.4145 GHz (channel 5 in theexample below).

For example, the FHSS system may use the following designatedfrequencies (with, for example, 500 KHz tolerance):

Channel Frequency 1   2402 MHz, 2   2404 MHz 3   2406 MHz, 4 2409.5 MHz5 2414.5 MHz 6 2419.5 MHz 7 2424.5 MHz 8 2429.5 MHz 9 2434.5 MHz 102439.5 MHz 11 2444.5 MHz 12 2449.5 MHz 13 2454.5 MHz 14 2459.5 MHz 152464.5 MHz 16 2469.5 MHz 17   2472 MHz 18   2474 MHz 19   2476 MHz 20  2478 MHz

Using these channels in any case, before consideration of anyinterfering external signal, will usually reduce interference on allwireless access points, whether focussed or not. The methods of theinvention will therefore build on this initial interference mitigationeffort.

Specific examples of implementations are:

Case 1: 802.11b (20 MHz Bandwidth)

WiFi channel is 1, Modulation is 802.11b

-   1. Channel 4,5—Reduce Channel Scanning Duty-   2. Channel 4,5—Change to Very Narrow Band

Case 2: 802.11gn (22 MHz Bandwidth)

WiFi channel is 3, Modulation is 802.11g, Bandwidth is 22 MHz

-   1. Channel 5,6,7,8 is Reduced Channel Scanning Duty-   2. Channel 5,6,7,8 is Changed to Very Narrow Band

Case 3: 802.11n (40 MHz Bandwidth)

WiFi channel is 3, Modulation is 802.11n, Bandwidth is 40 MHz

-   1. Channel 4,5,6,7,8 is Reduced Channel Scanning Duty-   2. Channel 4,6,8 is changed to very narrow Band

In this example (case 3) the bandwidth is 40 MHz (not 22 MHz), so thechannel spacing must be wider, hence only channels 4,6,8 are used.

Referring to FIG. 3 the dual mode radio communications device 104comprises the FHSS and DSSS modules 106, 108. As such, the dual moderadio communications device 104 is capable of communicating via eitheror both network type. The dual mode radio communications device 104 mayfurther comprise a memory 302 and a processor 304. The processor 304may, for example, provide processing capability to scan the signalsavailable to the DSSS module for detecting potential interference andwhere there is potential interference determine the at least one of theset of designated frequency channels used by the frequency hoppingspread spectrum system as having a property most similar to that of thesecond signal, and (or at least aiding) the FHSS module 106 withmodifying usage, by the frequency hopping spread spectrum system, of theat least one most similar designated frequency channel, for thecommunication of data. The dual mode radio communications device 104 mayalso comprise a RF mixer 306. Here it is shown as being external to theFHSS and DSSS modules 106 and 108. The RF mixer 306 is connected to theantenna 110 to allow communication of the signals to and from the dualmode radio communications device 104.

An example of an apparatus that may incorporate a dual mode radiocommunications device such as the dual mode radio communications device104 is a monitoring apparatus comprising an image capturing device, suchas a video camera. The monitoring apparatus may have both RF modulesworking in the 2.4 GHz band, one complying with the Wi-Fi standard andthe other using FHSS. Normally housing both RF modules together wouldmean they would “compete”. However the above-described systems andmethodology can be used to mitigate or remove such problems. Themonitoring apparatus may be used, for example, for home applications,such as baby, pet or security monitoring. Via the FHSS radio, image datacaptured by the image capturing device can be viewed on a specialmonitoring device within the home or via the Wi-Fi connection on anyconnected device, such as a smart phone, or tablet, anywhere outside thehome. Alternative apparatus, such as mobile security or communicationunits, could use the same principle, and communicate audio and/or videoover either or both radio schemes.

FIG. 4 shows monitoring apparatus in the form of an infant monitoringapparatus 210 comprising a portable receiver 212 and an infantmonitoring device 214. The infant monitoring device 214 is to be locatedat a first location, such as a bedroom, at which a infant has beenplaced, typically to sleep. The infant monitoring device 214 isconfigured to transmit infant monitoring data to the portable receiver212. The portable receiver 212 may be held by a user, such as a parentor other carer, at a second location remote from the first location. Thefirst and second locations may be on different floors of a building, orthe first may be within a building while the second is without.

Referring to FIGS. 4 and 5, the infant monitoring device 214 comprises abase 216 and a housing 218 mounted on the base. The connection 220between the housing 218 and the base 216 comprises an articulation sothat the housing can be moved relative to the base by a drive unitmounted in the housing. The drive unit comprises two motors 222, 224that can be powered to cause the housing to pivot about the X and Yaxes. The motors 222, 224 may be stepper motors. The drive unit furthercomprises a motor controller 228 to control actuation of the motors 222,224. The motor controller 228 may receive electric power from a powersupply unit 230 and actuate the motors 222, 224 in response to commandsignals issued by a device controller 232 in response to command signalsreceived from the portable receiver 212. The power supply unit 230 maydistribute electric power received from a mains supply via an ac/dcadapter provided in a plug 234 by which the infant monitoring device 214can be connected to a mains electric supply. In other examples, thead/dc adapter may be a part of the power supply unit 230. In someexamples, the power supply unit 230 may also distribute electrical powerreceived from a battery supply 236 housed in a compartment provided inthe infant monitoring device 214.

The infant monitoring device 214 comprises an image capturing device238. The image capturing device 238 comprises a video camera having oneor more lenses and a semi-conductor device that receives light via thelens(es) and records the received light electronically. Thesemi-conductor device may be a 1/6.5″ VGA CMOS image sensor. The imagecapturing device 238 is connected with the device controller 232. Thedevice controller 232 comprises a processor 240 that is operable toprocess digital video data output by the image capturing device 238 intodigital video frame data for transmission to the portable receiver 212.The processor 240 may be provided with an integral buffer memory tobuffer the digital video frame data. Alternatively, a separate buffermemory may be provided. The buffer memory may comprise volatile RAMprovided by an SRAM or DRAM module. The device controller 232 isconnected with a dual mode radio communications device 242 that isoperable to convert the digital video frame data into a format suitablefor wireless transmission to the portable receiver 212. The dual moderadio communications device 242 is configured to generate and transmitusing a FHSS format and another wireless format that is not the FHSSformat and employs interference mitigation as previously described topermit side by side transmission using the two formats. In some examplesthe dual mode radio communications device 242 may be a dual mode radiocommunications device as illustrated by FIG. 3 and the transmissions maybe in the 2.4 GHz waveband. In the example illustrated by FIGS. 4 to 8,the dual mode radio communications device 242 may be configured totransmit to the portable receiver 212 using the FHSS module and theportable receiver 212 is configured to receive signals generated usingthe FHSS format

The infant monitoring device 214 may further comprise a night visionunit 244. The night vision unit 244 may comprise a plurality of LEDsactivated automatically by a light sensor. In some examples, the nightvision unit 244 may be actuated by a clock signal from the devicecontroller 232 or a signal issued by the device controller in responseto a command signal issued by a user using a suitably equipped portablereceiver 212 (these optional or alternative modes are indicated in FIG.5 by a dashed line connection between the device controller 232 andnight vision unit 244). In the illustrated example, the night visionunit 244 comprises an array of eight LEDs disposed at equi-spacedintervals on a pitch circle diameter so as to surround the imagecapturing device 238.

The infant monitoring device 214 may further comprise an audio capturingdevice, such as a microphone 246. The microphone 246 may be incorporatedin the image capturing device 238. In examples in which a microphone isincluded in the image capturing device 238, the image capturing devicemay be provided with an audio codec to encode analogue audio data asdigital data for transmission to the portable receiver 212 with thedigital video data.

The digital video frame data and, where obtained, digital audio datatransmitted by the infant monitoring unit 214 comprises infantmonitoring data that is received by the portable receiver 212 and outputby the portable receiver 212 in a form a user can access so as to beable to monitor an infant's condition.

The infant monitoring device 214 may further comprise an audio outputdevice 248 (FIG. 5), such as a loudspeaker housed by the housing 218. Inexamples provided with an audio output device 248, the device controller232 may be provided with an audio codec and output interface so as to beable to output an analogue signal to the audio output device. The audiooutput device 248, when provided, can be used to output audio receivedfrom portable receivers 212 configured to transmit audio that is inputcontemporaneously by a user, or output soothing messages or other soundsstored in non-volatile memory accessible by the device controller 232.

Referring to FIGS. 4 and 6, the portable receiver 212 comprises ahandheld housing 256, a display 258(1), 258(2) and a non-contacttemperature sensing device 260 housed by the housing. The portablereceiver 212 may further comprise an audio output device 262, an audiocapturing device 264, a transceiver 266, a device controller 268 thatincludes a processor 270, an input interface 272 and a power supply 274.

The display may comprise a TFT LCD screen 258(1) to display video imagesderived from infant monitoring data received from the infant monitoringunit 214. The display may additionally comprise an audio level indicator258(2). The audio level indicator 258(2) may comprise an array of LEDsto provide a visual sound level indication for the audio output by theaudio output device 262 or the audio signal captured by the audiocapturing device 264. The array of LEDs may comprise a series of LEDsarranged in line.

The transceiver 266 is configured to receive infant monitoring datatransmitted by the infant monitoring device 214 and communicate it tothe device controller 268 in a form the processor 270 can process fordisplay via the screen 258(1). In examples in which the infantmonitoring device 214 is configured to transmit digital audio data tothe portable receiver 212, the device controller 268 is provided with anaudio codec and output interface for outputting an analogue signal tothe audio output device 262. The audio output device 262 may be aloudspeaker housed by the housing 256. Additionally, or alternatively,the audio output device 262 may be an output jack that allows theportable receiver 212 to be connected to an earphone or externalspeaker.

The audio capturing device 264 may comprise a microphone housed by thehousing 256.

The audio capturing unit 264 may be connected with the device controller268 to enable analogue audio data received from the microphone to beencoded as digital data for transmission by the transceiver 266 to theinfant monitoring device 214. Providing the portable receiver 212 withthis facility allows a user, to send soothing messages to the infant viaan audio output device of the infant monitoring device 214.

Referring to FIG. 7, the non-contact temperature sensing device 260 maybe housed by the housing 256 so as to point from a major face 280 of thehousing disposed opposite the major face 282 (FIG. 4) at which thedisplay 258 is visible. The temperature sensing device 260 may be aninfra red thermometer configured to output a digital signal indicativeof a sensed temperature. The digital signals output the by thetemperature sensing device 260 are communicated to the processor 270,which is configured to process signals from the temperature sensingdevice 260 and output a signal to the display that causes a temperaturereading to be displayed on the screen 258(1). In other examples, theportable receiver 212 may be provided with a further display device todisplay the temperature reading. However, it is convenient and economicto display the temperature reading using the screen 258(1).

Referring to FIG. 1, the interface unit 272 of the portable receiver 212may comprise a plurality of buttons to allow a user, to input commandsto the portable receiver. In the illustrated example, the interface unit272 comprises:

-   -   a power on/off button 284;    -   a video on/off button 286;    -   a temperature sensor on/off button 288;    -   an audio input device on/off and recording level adjustment        button 290; and    -   a multi-function pad 292 operable to provide volume +/− and        pan/tilt and zoom control inputs for the image capturing device        238.

The power supply 274 distributes electrical power received from abattery supply housed in a compartment housed by the housing 256 andaccessible via a cover 294 (FIG. 7) provided in the major face 280. Thebattery supply may be rechargeable by removal from the housing 256 andconnection with a suitable battery charger. Alternatively, the portablereceiver 212 may be provided with an input socket (not shown) to allowthe battery supply to be connected to a charger unit that may be a partof a plug (not shown) that can be plugged into a mains electrical supplyor allow the portable receiver to be plugged onto a charger cradle (notshown). In another example the battery supply may be recharged by aninductive charging system.

In use, a user can situate the infant monitoring device 214 in a room orarea in which an infant is to be left, typically to sleep and go toanother room or area with the portable receiver 212. The portablereceiver 212 can receive infant monitoring data transmitted by theinfant monitoring device 214 allowing the user to view the infant viathe screen 258(1) and hear sounds via the audio output device 262. Byoperation of the multi-function pad 292 the user can cause commandsignals to be transmitted to the infant monitoring device 214 to causethe image capturing device 238 to pan (pivot about the Y-Y axis), tilt(pivot about the X-X axis) or zoom in and out. The user can operate thebutton 290 to activate the audio capturing device 264 and send audiomessages to the infant via the audio output device 248 of the infantmonitoring device. Additionally, the user can take the portable receiver212 to the infant and operate the button 288 to activate the non-contacttemperature sensing device 260 and obtain a reading of the infant'stemperature, which will be displayed on the screen 258(1). This has theadvantage that the temperature reading can be obtained withoutdisturbing the infant and even in cases in which the infant is awake,avoids having to obtain the infant's cooperation in using a contacttemperature sensor such as a mercury thermometer. It s to be understoodthat while the temperature sensing device 260 is intended primarily forobtaining an infant's temperature, it can be used to obtain non-contacttemperature readings of other things.

Within a relatively short range, such as within a domestic environment,a user can monitor an infant using images or audio received by theportable receiver 212 from the infant monitoring device 214 bytransmission from the FHSS module of the dual mode radio communicationsdevice 242. If the user moves out of range of the FHSS transmissions,the user may continue to monitor the infant by means of transmissionsfrom the dual mode radio device 242 made by the other module andreceived by a mobile communications device, such as a smart phone ortablet. For example, the signal using the other module may be receivedby a wireless access point, such as a router, providing a wirelessinternet connection. Because the two radio transmission modules of thedual mode radio communications device 242 are able to transmit at leastsubstantially simultaneously, a baby sitter and parent may both be ableto receive transmissions from the infant monitoring device 214 allowingthem to both monitor the infant. For example, a parent may leave aninfant in the care of a baby sitter, who can monitor the infant usingthe portable receiver 212, and still be able to monitor the infant usinghis/her smart phone or tablet. Furthermore, because both radiotransmission modules can work side by side, it is not necessary for auser to remember to switch between the two, when for example, leavingthe coverage area of the FHSS module.

It is to be understood that a temperature sensing device is not anessential feature of the infant monitoring apparatus 210. Furthermore,the image capturing device may be configured to capture still imagesrather than video images. It is also not essential that the FHSS moduletransmits to a portable receiver as illustrated by FIGS. 4 and 6. Inprinciple, the FHSS module may transmit to any suitable device equippedto receive FHSS signals. For example, the FHSS module may transmit to adigital picture frame as disclosed by the Applicant's WO2012/104618. Itis also not essential that the infant monitoring device 214 has a driveunit to point the image capturing device. In other examples, theorientation of the image capturing device may be fixed. It is also to beunderstood that the infant monitoring apparatus 210 may be used tomonitor things other than infants in domestic and non-domesticapplications.

In the example illustrated by FIG. 3, the processor 304 is configured tooperate as a scanner to detect signals that may compete with the FHSSmodule. The processor 304 may operate software or firmware configured toprovide a scanner function or comprise a chip designed to incorporatethe scanning function. FIG. 9 illustrates a modification of the dualmode radio communications device of FIG. 3 in which a dedicated scanneris 308 is provided.

It will be appreciated by those skilled in the art that the inventionhas been described by way of example only, and that a variety ofalternative approaches may be adopted without departing from the scopeof the invention, as defined by the appended claims.

We claim:
 1. A method of mitigating interference with a first signalthat is a signal of a frequency hopping spread spectrum system,comprising: detecting, with a radio communications device, a secondsignal that is not a frequency hopping spread spectrum signal;determining, with the radio communications device, a property of saidsecond signal; determining, with the radio communications device, atleast one of a set of designated frequency channels used by saidfrequency hopping spread spectrum system as having a property mostsimilar to said property of said second signal; and modifying usage,with the radio communications device, of said at least one most similardesignated frequency channel by said first signal to communicate data soas to mitigate interference between said first and second signals byreducing a frequency bandwidth for the data of the first signal whensaid first and second signals are concurrently communicating on the atleast one similar designated frequency channel during simultaneoustransmission of said first and second signals.
 2. A method as claimed inclaim 1, wherein said property of said second signal is a frequencycharacteristic.
 3. A method as claimed in claim 1, wherein modifyingusage of said at least one most similar designated frequency channel bysaid first signal further comprises processing the data to reduce a databandwidth for communication via said at least one most similardesignated frequency channel.
 4. A method as claimed in claim 1, whereinsaid reduced bandwidth is less than 4.5 Mb.
 5. A method as claimed inclaim 4, wherein said reduced bandwidth is between 250 Kb and 1 Mb.
 6. Amethod as claimed in claim 1, further comprising reducing usage of saidat least one most similar designated frequency channel by said firstsignal by reducing usage of said at least one similar designatedfrequency in the frequency hopping spread spectrum system.
 7. A methodas claimed in claim 1, further comprising: detecting a change in saidproperty of said second signal; and re-determining said at least one ofsaid set of designated frequency channels having a property most similarto said property of said second signal; and modifying usage, by thefrequency hopping spread spectrum system, of said re-determined at leastone most similar designated frequency channel to communicate data so asto mitigate interference between said first and second signals duringsimultaneous transmission of said first and second signals.
 8. A methodas claimed in claim 1, further comprising, on detecting said secondsignal, determining frequencies for each of said set of designatedfrequency channels used by said frequency hopping spread spectrum systemaccording to the type of said second signal.
 9. A radio communicationsdevice, said device comprising: a first module configured to generate afrequency hopping spread spectrum signal to communicate data; a scannerconfigured to detect a second signal that is not a frequency hoppingspread spectrum signal; and a processor configured to: determine aproperty of said second signal; determine at least one of a set ofdesignated frequency channels used by said frequency hopping spreadspectrum module as having a property most similar to said property ofsaid second signal; and said first module is further configured tomodify usage of said at least one most similar designated frequencychannel by said frequency hopping spread spectrum signal to communicatedata so as to mitigate interference between said frequency hoppingspread spectrum signal and said second signal by reducing a frequencybandwidth for the data of the frequency hopping spread spectrum signalwhen said frequency hopping spread spectrum signal and second signal areconcurrently communicating on the at least one similar designatedfrequency channel during simultaneous transmission of said frequencyhopping spread spectrum signal and said second signal.
 10. A radiocommunications device as claimed in claim 9, further comprising a secondmodule configured to generate a further signal, additional to saidfrequency hopping spread spectrum signal, to communicate with a devicegenerating said second signal.
 11. A radio communications device asclaimed in claim 10, wherein said device generating said second signalis a router configured to provide internet access.
 12. A monitoringapparatus comprising at least a monitoring device, the monitoring devicecomprising: at least one image capturing device configured to captureimage data; and a dual mode radio communications device comprising: afirst module configured to generate a first signal using a frequencyhopping spread spectrum format to communicate data derived from saidimage data; a second module configured to communicate with a device thatgenerates a second signal that uses formats other than said frequencyhopping spread spectrum format; a processor configured to: detect anddetermine a property of said second signal; and determine at least oneof a set of designated frequency channels used by the first module ashaving a property most similar to that of said second signal; and saidfirst module is further configured to modify usage of the at least onemost similar designated frequency channel by said first signal tocommunicate said data so as to mitigate interference between said firstand second signals by reducing a frequency bandwidth for the data of thefirst signal when said first and second signals are concurrentlycommunicating on the at least one similar designated frequency channelduring simultaneous transmission of said first and second signals.
 13. Amonitoring apparatus as claimed in claim 12, wherein said monitoringdevice generating said second signal is a router configured to provideinternet access.
 14. A monitoring apparatus as claimed in claim 12,further comprising a portable receiver configured to receive said firstsignal transmitted by said first module and having a display to displayimages derived from said data communicated by said first signal.
 15. Amonitoring apparatus as claimed in claim 14, further comprising an audiocapturing device, within the monitoring device, configured to captureaudio data associated with said image data, wherein said datacommunicated by said first signal includes data derived from said audiodata and said portable receiver comprises an audio output device tooutput audio derived from said data communicated by said first signal.16. A monitoring apparatus as claimed in claim 14, wherein said portablereceiver further comprises an input device to receive user inputcommands to control said at least one image capturing device andconfigured to transmit command signals based on said user input commandsto said at least one image capturing device using said frequency hoppingspread spectrum format.
 17. A monitoring apparatus as claimed in claim14, wherein said portable receiver further comprises a non-contacttemperature sensing device.
 18. A monitoring apparatus as claimed inclaim 12, wherein said second module is further configured to generatesaid second signal using a direct sequence spread spectrum format.